This invention relates to the field of urological methods and devices, and more particularly to such methods and devices as are used in the treatment of urethral stenoses. More specifically, the present invention relates to a urethral stent, and to a method and apparatus for inserting and locating the stent in a human male urethra to treat the stenosis therein.
Stenosis (partial occlusion) of the human male urethra, resulting from disease or injury, is typically treated by surgery. Conventional surgical techniques, such as dilation or commissurotomy, however, often offer only temporary or partial relief, since it is not uncommon for the stenosis to reoccur. Alternative treatments for such stenoses or strictures, that wound maintain urethral patency for extended periods, have, therefore, been sought.
One approach for providing long-term relief for urethral stenoses is the implantation of a urethral stent. Urethral are known in the art, as exemplified by U.S. Pat. No. 4,762,128 --Rosenbluth and U.S. Pat. No. 4,893,623--Rosenbluth, both commonly assigned to the assignee of the present application. The Rosenbluth patents both relate to methods and apparatus for the treatment of prostatic hypertrophy, wherein a urethral stenosis caused by a hypertrophied prostate gland is relieved by the implantation of a stent in the stenotic region of the urethra. The stents disclosed in the Rosenbluth patents, however, are in the form of radially expandable metallic tubes that are specifically adapted for implantation in the prostatic region of the urethra by means of a balloon catheter, and that, once in place, can withstand the radial pressures exerted by the hypertrophied prostate. Such stents may be less well-suited for implantation in the penile portion of the urethra (where many strictures occur), where less radial rigidity is needed, and where greater flexibility may be desired.
An alternative stent configuration is that of a helically-coiled spring, such as that disclosed in U.S. Pat. No. 4,553,545 --Maass et al. The helically-coiled stent disclosed in the Maass et al. patent is made of a stainless steel or the like, and is specifically adapted for implantation as an intravascular prosthesis. To this end, the Maass et al. patent discloses a device for implanting the stent in a blood vessel. This implantation device, however, is not suitable for implantation of the stent in a bodily lumen, such as the urethra, for a number of reasons, including the lack of means for visualizing the location of the stent within the enclosed lumen during implantation.
The particular physiology and structure of the penile urethra make it desirable to maximize the suppleness and flexibility of the stent, without sacrificing its ability to restore urethral patency by radially expanding the stenotic region To this end, certain biocompatible polymeric materials may offer significant advantages over the metallic materials disclosed in the Rosenbluth and Maass patents discussed above.
Among such polymeric materials, there exist a number of biodegradable or resorbable polymers that, upon implantation, gradually are absorbed by the body and replaced by living tissue, or that, when implanted in the urethra, would be dissolved by the urine flowing therethrough. At least two such materials are known and are widely-used for implanted devices: Polyglycolic Acid (PGA) and Polylactic Acid (PLA). See, for example, U.S. Pat. No. 3,620,218 --Schmitt et al. (PGA); and U.S. Pat. No. 3,887,699 --Yolles (PGA and PLA). U.S. Pat. No. 4,674,506--Alcond discloses an anastamosis stent made of PGA.
U.S. Pat. No. 4,950,258 --Kawai et al. discloses a coil-shaped molded article, made from homopolymers or copolymers of lactides or glycolides, that can be used as a biodegradable vascular implant to open up an obstructed blood vessel. The coiled article would be deformed for insertion into the blood vessel, and then heated. The application of heat would cause the article to return to its original shape. Depending on the specific shape and composition of the article, and the processes used for forming it into its original shape and giving it a "shape memory", temperatures in the range of 36 degrees Centigrade to 65 degrees Centigrade would apparently need to be applied to restore the article to its original shape in 10 seconds or less. The need to apply heat for shape restoration is disadvantageous, because it would complicate the insertion procedure, would require specialized heating implements (not disclosed in the Kawai et al. patent) during insertion, and would require care not to exceed a degree of heating (temperature and time duration) that could result in tissue damage.
As yet, the prior art has not contemplated the use of bioresorbable materials in the formulation of a helically-coiled urethral stent that does not depend upon the application of heat for shape restoration, nor has there been developed a suitable apparatus or method for the implantation of a helically-coiled stent in the penile urethra.